This invention relates to a poly(4-methyl-1-pentene) composition which is resistant to food stains and colored white without the need for a pigment. It also relates to white colored dishes having improved resistance to food stains.
The term "dish" is used herein in its broadest sense to designate all open containers for holding or serving food, including ordinary dishes, bowls, platters, cups, and other tableware used in serving food.
Most reusable dishes used in school lunch, cafeterias or the like are made of polypropylene because of its handling advantages of being lightweight, unbreakable, and durable. One consideration for reusable plastic dishes is the resistance to food stains that dishes having food adhered can be readily washed away of the food without being discolored. If dishes having curry, ketchup, barbecue or other sauces deposited for a long time can be readily cleaned up by washing, schools and other cafeterias which must deal with a great number of dishes can get an economic saving by reducing the time and labor consumed in washing. With the recent widespread use of microwave ovens, plastic dishes are now required to be microwave proof. Conventional polypropylene dishes have the drawbacks that they are not satisfactorily resistant to food stains and are too weakly heat resistant to be put in microwave ovens.
The lack of heat resistance can be overcome by the use of polycarbonate and polysulfone resins, which are still insufficient in resistance to food stains. Poly(4-methyl-1-pentene) has sufficient heat resistance and electrical properties to be used in microwave ovens and is resistant to food stains. Dishes molded from poly(4-methyl-1-pentene) are thus fully resistant to food stains and to cooking in microwave ovens.
Dishes, particularly on their surface, on which food is served, are often colored white for aesthetic and appetizing reasons. Since poly(4-methyl-1-pentene) is transparent as is well known in the art, the inventors attempted to impart a white color to dishes of poly(4-methyl-1-pentene). Various pigments are generally used to color resins white. The inventors blended a pigment or similar filler in poly(4-methyl-1pentene) to find that the filler adversely affects one of the features of poly(4-methyl-1-pentene), resistance to food stains.